One of the most important soil physical relationships requiring estimation is the amount of water available in the soil represented by a water retention curve. A water retention curve represents the relationship between soil water tension (matric potential) and soil water content of the soil. Many models have been developed to estimate the amount of water available in soil from small farmlands to large-scale catchments. The soil water retention curve plays a major role in many of these models. Studies of water balance and runoff generation leading to sediment production require the calculation of a soil water retention curve at the lower end (0 to 100 cm soil water tension).
The most popular and only reliable method to obtain the soil water retention curve at the lower tension is a tension plate with a hanging water column. This method has been in use for over 70 years. A tension plate is made from a porous material such as ceramic or a sand bed. Since larger pore space dominates the soil water characteristics at the lower tension range, tests must be carried out with either minimum or no disturbance to the soil sample.
To use the tension table, the soil sample must first be saturated. During saturation, the weight of the soil sample is checked regularly to find the equilibrium point. Once the saturation process is completed, different tensions are applied to the soil sample, which sits on the tension plate, by the hanging water column. In order to find the equilibrium point for each applied tension, the water meniscus in the hanging water column is monitored regularly. This is a very time consuming task. Once the soil sample reaches equilibrium, it is transferred to a weighing apparatus at the end of each tension step to estimate the moisture content.
The main disadvantages of this method are:                1. Disturbance to the fragile soil matrix (larger pore structure) due to regular handling of the soil sample.        2. Inaccurate soil moisture estimation due to sample handling.        3. High labour intensity. Regular supervision is necessary to determine the equilibrium points.        
It would be useful to at least partially automate the test procedure to eliminate or reduce the drawbacks. An added advantage of an automated system could be the ability to produce accurate outflow data to estimate the unsaturated hydraulic conductivity.